The present invention relates to an optical recording medium using a chelate dye comprising azo compounds and a metal in a recording layer.
Since optical recording using a laser enables high density storing and reproduction of data, the development has been advanced in particular in recent years. As the media for use for optical recording, a magneto-optical recording medium, a phase-change optical recording medium, and an organic dye optical recording medium have been conventionally proposed.
Of these media, an organic dye optical recording medium has been considered to be superior in view of inexpensiveness and simple manufacturing process.
Examples of organic dye optical recording media include a recordable compact disc (CD-R) comprising an organic dye layer having laminated thereon a metal layer having high reflectance which is capable of overwriting can be exemplified.
As the dyes for a recording layer of CD-R, various dyes, e.g., cyanine dyes, phthalocyanine dyes, metal chelate dyes, etc., have been proposed and put to practical use. Focusign on the metal chelate dyes excellent in light fastness and environmentally durable, the present inventors have proposed many optical recording media using metal chelate dyes, including a domestic re-publication No. 3-818057 of PCT international patent publication, and JP-A-6-65514 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d).
In general, the optical recording medium is required to have good storage stability, high light fastness, broad margins, such as recording power, and a high reflectance. The dyes themselves to be used for optical recording media are also required to have performances capable of realizing these characteristics.
However, it has so far been very difficult to satisfy these characteristics at the same time.
Even when a plurality of dyes are used in combination so as to compensate for mutual weak points, the properties of a dye inferior in properties are generally liable to be revealed strongly. Accordingly, merely mixing dyes is insufficient to improve the performances of the optical recording medium.
As a result of extensive studies for attaining these objects, the present inventors have found that a plurality of performances required of the optical recording medium can be improved at the same time by using, in the recording layer, an azo metal chelate dye comprising a plurality of azo compounds having different structures coordinated to one metal.
That is, the present invention was achieved by an optical recording medium comprising a substrate and a laser-writable and/or readable recording layer provided thereo, wherein the recording layer contains a chelate dye comprising two or more azo compounds having different structures and a divalent or more metal ion, and the azo compounds are selected from the azo compounds represented by the following general formula (I) and the general formula (II): 
wherein ring A represents an aromatic heterocyclic ring which may have substituent(s); ring B represents an aromatic hydrocarbon ring, an aromatic heterocyclic ring, or a condensed ring of one of these rings with saturated ring(s), and these rings each may have substituent(s) other than X; and X represents a group having an active hydrogen; 
wherein ring C represents an aromatic heterocyclic ring which may have substituent(s); ring D represents an aromatic hydrocarbon ring, an aromatic heterocyclic ring, or a condensed ring of one of these rings with saturated ring(s), and these rings each may have substituent(s) other than X; and X represents a group having an active hydrogen.